Are nullable types reference types?

Question

When I declare an int as nullable

int? i=null;

Does i here become a reference type?

Answer 1

No, a nullable is a struct. What is happening is that the nullable struct has two values:

1. The value of the data type ( int for int? , DateTime for DateTime? , etc.).
2. A boolean value which tells if the data type value has been set. ( HasValue is the property.)

When you set the value of the data type, the struct changes HasValue to true.

Nullable types (C# Programming Guide)

Answer 2

From Nullable Types (C# Programming Guide) :

Nullable types are instances of the System.Nullable struct.

and

Nullable types represent value-type variables that can be assigned the value of null. You cannot create a nullable type based on a reference type. (Reference types already support the null value.)

So, no they're not reference types.

Answer 3

Nullable types are neither value types nor reference types. They are more like value types, but have a few properties of reference types.

Naturally, nullable types may be set to null . Furthermore, a nullable type cannot satisfy a generic struct constraint. Also, when you box a nullable type with HasValue equal to false , you get a null pointer instead of a boxed nullable type (a similar situation exists with unboxing).

These properties make nullable types non-value types, but they sure aren't reference types either. They are their own special nullable-value type.

Answer 4

No, the Nullable type is in fact a struct. The runtime will intelligently handle the setting of a null value for you, giving the appearance of a reference type, when it's not....

Answer 5

Nullable types cannot be reference types.

http://msdn.microsoft.com/en-us/library/2cf62fcy.aspx

Answer 6

您不应该将引用类型设置为可空类型，因为您可以在其位置传递null。